Asthma Symptoms Increase With Higher Indoor Particle Levels

This recent study provides some insight into the relationship of indoor air quality and respiratory health. It is clear that higher indoor air pollution leads to an increase in the severity of asthma symptoms. But do we really know any more about what leads to the problems and what to do about it?

Researchers from Johns Hopkins University have found an association between higher indoor particle levels and increases in asthma severity in children. Their study published in the February 2009 edition of Environmental Health Perspectives is one of the first to analyze indoor pollution levels and respiratory health outcomes. (“In-Home Particle Concentrations and Childhood Asthma Morbidity,” M. McCormack, P. Breysse, E. Matsui, N. Hansel, D. Williams, J. Brosnan, P. Eggleston, G. Diette; 117: 294-298).)

The researchers followed 150 asthmatic children from inner-city neighborhoods in Baltimore. The children were aged 2 to 6. Their environments were analyzed for 6 months. Ninety-one percent of the participants were African-American from lower socio-economic backgrounds and spent most of their time indoors.

Air measurements were taken in the children’s homes to determine both fine particle (less than 2.5 micrometers in diameter) and coarse particle (between 2.5 and 10 micrometers in diameter) concentrations. The measurements were taken over a three day period at the start of the study, after 3 months and at 6 months.

There were some striking correlations between indoor particle concentrations and increased asthma symptoms. For every 10 micrograms per cubic meter of air (ug/m3) increase in coarse particle concentration, there was a 6 percent increase in the number of days of cough, wheeze, or chest tightness. For every 10 ug/m3 increase in fine particle concentrations there was a 7 percent increase in wheezing severe enough to limit speech and a 4% increase in days when rescue medication was needed. In many cases the levels of fine particle concentrations were twice as high as the outdoor limits set by the EPA.

While the study gives greater weight to the arguments to clean-up indoor air, it has its limitations. The fact that the Johns Hopkins team found a relationship between higher particle counts and increased asthma symptoms is not particularly helpful in terms of determining what exactly needs to be done to accomplish the goal of better indoor air quality.

For example, what actually was going on in those homes that had the much higher particle concentrations? Was there smoking by inhabitants? Were the windows open most of the time? What were the outdoor particle counts? Were there visible signs of mold or cockroach infestation? How close were the study participants living to freeways or other sources of air pollution? What was the chemical composition of the particles measured?

A recurring problem in Indoor Air research is “connecting the dots” between specific indoor behaviors and actions and health outcomes. This study comes tantalizingly close to providing information on specific steps that could be taken. Instead it just confirms our knowledge of the general problem of indoor air pollution and respiratory health. Hopefully, follow-up studies by this team will address these issues.